Conventionally, a turret tool rest having a hollow rotating shaft which rotates a turret on which a tool is to be mounted, a hollow intermediate shaft arranged within this rotating shaft, and a driving shaft of a rotating tool to be mounted on the turret has been known (see Patent Document 1, for example).
Further, in general, when processing a work by means of a tool mounted on a turret tool rest, a coolant is supplied to the tool mounting part of a turret on which the tool is mounted, and the coolant is supplied from the tool mounting part to the part of the work to be processed by means of the tool (see Patent Document 2, for example).
The supply structure of a coolant to the tool mounting part disclosed in Patent Document 2 has a configuration in which a coolant supply pipe inserted into the hollow driving shaft of the rotating tool is served as a coolant passage.
The above-mentioned coolant supply pipe has a defect that, since a coolant passes within the pipe, the central part of the intermediate shaft into which the coolant supply pipe is inserted cannot be effectively utilized as a space. Further, since the coolant supply pipe is required to be inserted into the innermost shaft, a shaft with the smallest diameter is required to be hollow.